Distributed system for radio frequency environment simulation

ABSTRACT

In some embodiments, an electromagnetic measurement system to perform radio frequency, RF, downlink testing of a device under test, DUT, in a chamber is provided. Exterior to the chamber is an emulator core configured to introduce an impairment in each of at least one transmit signal to produce at least one impaired signal for each of at least one emulated channel. Within the chamber, for each of the at least one emulated channel, an up-converter is configured to up-convert an impaired signal of the emulated channel to produce a radio frequency, RF, signal.

TECHNICAL FIELD

This disclosure relates to a method and system for emulating channels ina radio frequency (RF) communication system including systems thatoperate in the micro-wave and milli-meter wave frequency ranges.

BACKGROUND

U.S. Pat. No. 8,331,869 describes systems and methods for over-the-airperformance testing of wireless devices with multiple antennas. Thisclass of system, referred to as a boundary array system, reproduces aradiated near-field environment that appears to the device in the testvolume as though it originated in the far field and had the multipathcharacteristics of a chosen emulated environment.

FIG. 1 is a typical multiple input multiple output (MIMO) boundary arrayconfiguration 10 for a test of a device under test (DUT) 22, showingboundary array antennas 12 in an anechoic chamber 14 with a wirelesscommunication tester 16 connected through a spatial channel emulator 18and amplifiers 20. Splitters 28 may be interposed between the wirelesscommunication tester 16 and the spatial channel emulator 18. Someconfigurations require multiple individual channel emulatorssynchronized together to produce sufficient output channels to drive allof the antenna elements in the chamber. The test configuration of FIG. 1is typically used to evaluate the receiver performance of DUT22. Whenthe DUT 22 is a cellular phone, for example, the test configuration ofFIG. 1 would evaluate the downlink signal from the base station to themobile phone. When the DUT 22 is a base station, for example, the testconfiguration of FIG. 1 is would evaluate the uplink signal from themobile phone to the base station. For simplicity, this document willrefer to the DUT receiver test configuration as the downlink, and theDUT transmit test configuration as the uplink. The configuration of FIG.1 is uni-directional for simplicity. Bi-directional systems are alsoemployed.

The device under test (DUT) 22 is positioned on a positioner, such as aturntable, within a test volume of the anechoic chamber 14 that isisolated from the environment exterior to the anechoic chamber 14 by RFabsorber lined walls, floor and ceiling. The array of antennas 12radiate electromagnetic energy (radio waves) toward the DUT in a varietyof directions. The radiated signals from each of the antennas 12 havevarious impairments (delay spread, Doppler, interference, etc.) appliedthrough spatial channel emulator 18 to simulate multipath fading in areal world environment.

The various impairments are introduced into signals received from thewireless communication tester 16 by one or more spatial channelemulators 18 that digitize the received signals. The digitized receivedsignals are delayed and weighted in amplitude by the spatial channelemulator 18. More particularly, the spatial channel emulator 18 may addmultipath delay, delay spread, fading, interference, and otherimpairments common in typical radiated communication paths, and thenconverts the result to analog signals and up-converts the result to aradio frequency, RF. Thus, each output of the spatial channel emulators18 may be the sum of multiple replicas of the input signal delayed andweighted according to a channel model definition, and will vary in timebased on a motion definition that models relative motion of the DUT 22or an intervening reflector. Doppler frequency shift may also beintroduced arising from the relative motion. Interference may also beintroduced by adding additive white Gaussian noise (AWGN) or other noiseas well as by injecting specific interfering signals. The full panoplyof channel effects emulated by the channel emulator are referred toherein collectively as impairments.

In a typical configuration, the number of inputs to the spatial channelemulator 18 may be different from the number of outputs of the spatialchannel emulator 18. Splitters 28 may be interposed between the wirelesscommunication tester 16 and the spatial channel emulator 18. Each outputof the spatial channel emulator 18 is amplified by a power amplifier 20and directed on a path, typically provided by cables, to an antenna 12.The spatial channel emulator emulates a plurality of channels, eachchannel being associated with a different one of the antennas 12.

Amplification is required between the spatial channel emulator 18 andthe antennas 12 in order to produce sufficient radiated power to bereceived by the DUT on the downlink and to amplify the weak signalsreceived from the DUT to be well above the receiver sensitivity of thechannel emulator on the uplink. The wireless communication tester 16emulates an end of a radio link opposite the DUT. The uplink is the pathof signal propagation from the DUT 22 to the wireless communicationtester 16 (these paths not being shown in FIG. 1).

The wireless communication tester generates signals according to acommunication protocol of the DUT. For example, the wirelesscommunication tester 16 may generate transmit signals that are formattedfor long term evolution (LTE) signaling, and may receive signals fromthe DUT that are also formatted for LTE signaling. Other communicationprotocols, such as Wi-Fi, may be employed by the wireless communicationtester 16. Also shown is a communication antenna 24 coupled to a lownoise amplifier (LNA) which is connected to the wireless communicationtester 16. The purpose of the communication antenna 24 is to provide analternate, un-faded and potentially low loss communication path betweenthe DUT and the communication tester for signals that are unrelated tothe metric being tested on the DUT (e.g. closed loop feedback of adigital error rate during a receiver sensitivity test) in order tomaintain the full communication link.

FIG. 2 is an implementation of one example of an RF channel emulator 18that includes emulator receivers (vector signal analyzers) 30 andemulator transmitters (vector signal generators) 32 around a digitalsignal processing channel emulator core 34. In the channel emulatorcore, each signal may be impaired and added to other signals to produceimpaired signals in order to simulate the effects of one or more signalspropagating over the air, being reflected off of obstacles such asbuildings, and arriving at the DUT with different amplitudes and phases.Doppler shift may also be introduced by the channel emulator core 34.

Common components of the emulator receivers 30 are shown in FIG. 3. Alow noise amplifier 36 receives an RF signal, possibly having a low SNR,and amplifies the RF signal and optionally passes the amplified RFsignal to a further amplification stage that includes a variable gainamplifier 38. The amplified RF signal is down-converted in a mixer 40with a local oscillator (LO) signal from an LO 42 to produce anintermediate frequency (IF) or baseband signal that is filtered by afilter 44, and possibly further amplified by an amplifier 46. The signaloutput of the amplifier 46 is an analog signal which may be converted toa digital signal by an analog to digital converter (ADC) 48.

Common components of the emulator transmitters 32 are shown in FIG. 4that include a digital to analog converter (DAC) 50, a filter 52, and anamplifier 54. The signal that passes through these components may be atbaseband or at an intermediate frequency. The signal is then mixed in amixer 56 with a local oscillator signal from an LO 58. The output of themixer is an RF signal that may be further amplified by a variable gainamplifier (VGA)60.

FIG. 5 is a single emulated downlink channel between a wirelesscommunication tester 16 and a DUT 22. (For simplicity, we shall call thedirection of propagation of FIG. 5 the downlink direction). In thedownlink, the wireless communication tester 16 generates transmitsignals to be received over the air by the wireless device, DUT 22. Thetransmit signals from the wireless communication tester are routed tothe spatial channel emulator 18 a by signal routing 62 a, which may be,for example, coaxial cables, and switches that would enable switching tocalibration paths or other test paths (not shown) in order to provideflexibility to alter the configuration as desired. Note that there maybe any number of RF paths between the wireless communication tester 16and the spatial channel emulator 18 for multiple input multiple output(MIMO) or diversity testing, all of which are combined into a single RFpath for each antenna element at the output of the spatial channelemulator 18.

The spatial channel emulator 18 a replicates each signal received fromthe communication tester 16, impairs each replica in a different way,and combines the impaired replicas to produce an impaired signal of thechannel. Note that the applied impairments may simulate multipatheffects as well as Doppler shift and other time and frequency dependenteffects. The impaired signal output by the spatial channel emulator 18 ais an RF signal that is coupled by signal routing 62 b to an amplifier64 to be amplified. The output of the amplifier 64 is routed to theanechoic chamber 14 to the antenna 12 by signal routing 62 c. Theantenna 12 radiates the impaired signal to the device under test 22.Note that the signals carried by the signal routing, herein referred tocollectively as signal routing 62, are RF signals, and thus, may exhibitsignificant losses.

FIG. 6 is a single emulated uplink channel between a DUT 22 and awireless communication tester 16. (For simplicity, we shall call thedirection of propagation of FIG. 6 the uplink direction). Signalsradiated by the DUT 22 are received by the antenna 12 which converts theelectromagnetic radiation (radio waves) to an RF signal which isamplified by a low noise amplifier (LNA) 36. The RF output of the LNA 36is coupled out of the anechoic chamber 14 to the spatial channelemulator 18 b by signal routing 62 d. The spatial channel emulator 18 bmay apply different impairments to replicas of the received RF signal toform impaired signals to simulate a multipath, Doppler-shiftedenvironment. The output of the spatial channel emulator 18 b is at leastone output signal that is coupled by signal routing 62 e to the wirelesscommunication tester 16.

Note once again that the signal routing 62 carry RF signals, and thus,the signal routing 62 introduce significant losses. As with the downlinkchain of FIG. 5, in the uplink configuration of FIG. 6, there may be anynumber of RF paths between the spatial channel emulator 18 and thewireless communication tester 16 for MIMO or diversity testing. The RFpaths may be derived from a single RF signal at the input of the spatialchannel emulator 18.

Note that bidirectional channel emulation can be performed with twoseparate, synchronized channel emulators 18 a and 18 b or as a singlebi-directionally configured unit. Each channel emulator block may alsobe realized by a plurality of channel emulators, referred to hereincollectively as spatial channel emulators 18.

While the boundary array technique is a powerful mechanism that cantheoretically produce any desired RF environment, the capabilities ofcurrently available RF test equipment provide physical, practical, andfinancial limits to what can be achieved with the system.

The ability to produce a uniquely correlated spatial distribution withinthe test volume is governed by the same Nyquist theorem limitations ofnear-to-far-field conversion, whereby a spherical surface surroundingthe DUT should have at least two sampling points (antenna directions)per wavelength along the surface of the sphere. The larger the antennaseparation or general RF interactive region on the DUT, the more activeantennas are needed in the boundary array in order to produce the properRF environmental conditions.

In addition to the physical constraints of the antenna size around theperimeter of the test volume, which forces a larger array diameter asthe number of antennas 12 increases, the number of amplifier and channelemulator resources required increases by as much as four times thenumber of antenna locations. Since each antenna location may be calledupon to support two antenna elements in orthogonal polarizations (i.e. adual polarized antenna), and assuming bi-directional communication, eachantenna location requires four amplifiers connected to two channelemulator transmitters and two channel emulator receivers remote from theantenna locations. In addition, for full spherical coverage, the numberof required antennas increases as the square of the frequency to betested multiplied by the maximal radial extent (MRE) dimension of theDUT, i.e. N∝(f r)² or N∝(r/λ)², where r is the radial dimension, N isthe number of antennas, and A is the wavelength. Stated simply, as thetest frequency and/or DUT size increases, the number of requiredantennas increases.

Since RF channel emulators 18 were originally designed for conductedtesting of radio transmitters and receivers, adapting them for use inover-the-air testing conditions requires the addition of amplificationto overcome the losses associated with RF cables, antenna efficienciesof both the boundary array antennas 12 and antennas of the DUT 22, andfree-space path losses due to the range length. Since the poweramplifiers 20 are independent of the power control of the spatialchannel emulator 18, they must provide highly linear performance inorder to generate the expected power levels within the test volume.

Likewise, since power control occurs before amplification on thedownlink, the desired signal level moves closer to the instrumentationnoise floor and then both signal and noise are amplified and injectedinto the chamber, where the instrumentation noise may become asignificant portion of the signal-to-noise ratio (SNR) seen at the DUTreceiver. The noise figure of the power amplifier is also added to thenoise of the channel emulator and other instrumentation, therebydecreasing the SNR.

Similarly, on the uplink, the signal received at the boundary arrayantenna 12 from the DUT 22 is well below the signal level expected atthe input to the spatial channel emulator 18, so low noise amplificationis required to boost it above the receiver sensitivity of the spatialchannel emulator 18. Since cable losses associated with bringing thesignal out of the anechoic chamber 14 to the spatial channel emulator 18input add to the loss, the resulting negative impact on signal to noiseratio is increased.

Also, bi-directional communication where both downlink and uplinksignals are present simultaneously requires the introduction of someform of isolation to ensure that the high power output of the downlinkamplifier is not coupled into the highly sensitive input of the lowernoise amplifier. Any cross coupling between the two amplifiers canseverely degrade system performance and is highly likely to cause damageon the uplink side, either at the amplifier and/or the input to thechannel emulator 18 b.

Since conventional spatial channel emulators 18 are large rack mountpieces of test equipment that reside outside the shielded anechoicchamber 14, as the number of antenna locations increases, not only doesthe range length increase, but the required length of all cables betweenthe channel emulators 18 and amplifiers 20 and the boundary arrayantennas 12 generally increases by at least π times the increase inradius. While the free-space path loss increases logarithmically withthe increase in radius, the loss of an RF cable is a linear function ofthe cable length. Thus, eventually the cable losses can dominate thelosses of the system as the system is scaled up to include morechannels.

Conversely, in suitable instrumentation amplification, there is an upperlimit to the output power of a single power transistor, so thatincreasing the amplification to overcome additional path loss becomes aproblem of parallel amplification rather than series amplification, withthe associated complexities of combining the power at the output. Theresult is that the associated size, cost, heat generation, etc. for thelarger amplifiers grows exponentially as the linear output powerincreases. Finally, the number of required RF cables also increases bythe same four times the number of probe positions that the amplifiersand channel emulation must increase.

As to the wireless communication tester 16, the process of generating anRF signal and then tuning and digitizing it in order to perform thechannel emulation via the spatial channel emulator 18 introducesadditional error and uncertainty into the signals for both uplink anddownlink.

Thus, one problem with existing systems is the RF path loss associatedwith the distances involved and the amplification required to overcomethese losses. The use of existing centralized RF channel emulatorsdesigned for conducted testing coupled with the expensive high poweramplifiers needed to overcome this path loss results in most of theexpense of the amplification being spent to heat up the RF cables due tointernal losses.

SUMMARY

In some embodiments, an electromagnetic measurement system to performradio frequency, RF, downlink testing of a device under test, DUT, in achamber is provided. Exterior to the chamber is an emulator coreconfigured to introduce an impairment in each of at least one transmitsignal to produce at least one impaired signal for each of at least oneemulated channel. Within the chamber, for each of the at least oneemulated channel, an up-converter is configured to up-convert animpaired signal of the emulated channel to produce a radio frequency,RF, signal.

In some embodiments, the system further includes, for each of the atleast one emulated channel, an antenna configured to radiate the RFsignal. In some embodiments, the chamber is one of an anechoic chamberand a reverberation chamber. In some embodiments, an impairment includesat least one of an amplitude weighting and a temporal shift. In someembodiments, the system includes, exterior to the chamber, for each ofthe at least one emulated channel, a digital to analog converter toconvert an impaired signal from the emulator core from a digital form toan analog form. In some embodiments, the system includes, within thechamber, for each of the at least one emulated channel, a variable gainamplifier configured to adjustably amplify the RF signal.

In some embodiments, the impaired signal is mixed with an LO signal toproduce an intermediate frequency signal. In some embodiments, theimpaired signal is mixed with the LO signal to produce a basebandsignal. In some embodiments, the system further includes, within thechamber, for each of the at least one emulated channel, a digital toanalog converter, DAC, configured to convert an impaired signal from adigital form to an analog form such that the analog form of the impairedsignal is up-converted.

In some embodiments, an electromagnetic measurement system to performradio frequency uplink testing of a device under test, DUT, in a chamberis provided. The system includes, within the chamber, for each of atleast one emulated channel, a down-converter configured to down-convertan RF signal received via an antenna from the DUT to produce adown-converted signal for the emulated channel. The system furtherincludes, exterior to the chamber, an emulator core configured tointroduce an impairment in each of at least one down converted signalreceived from the at least one emulated channel to produce at least oneimpaired receive signal.

In some embodiments, the chamber is one of an anechoic chamber and areverberation chamber. In some embodiments, the system further includes,for each of the at least one emulated channel, an antenna. In someembodiments, the impairment is at least one of an amplitude weightingand a temporal shift. In some embodiments, the system includes, withinthe chamber, for each of the at least one emulated channel, a variablegain amplifier within a path of a received RF signal to adjustablyamplify the RF signal. In some embodiments, the down-converted signal isat an intermediate frequency, IF. In some embodiments, thedown-converted signal is at baseband. In some embodiments, the systemincludes, within the chamber, for each of the at least one emulatedchannel, an analog to digital converter, ADC, configured to convert thedown-converted signal from analog form to digital form.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, in a chamber is provided. Within the chamber,for each of at least one emulated channel, an emulator core isconfigured to introduce an impairment in each of at least one transmitsignal to produce an impaired signal. A radio frequency, RF, transmitteris configured to up-convert the impaired signal to produce a radiofrequency, RF, signal.

In some embodiments, the chamber is one of an anechoic chamber and areverberation chamber. In some embodiments, the impairment is at leastone of an amplitude weighting and a temporal shift. In some embodiments,the system includes, for each of the at least one emulated channel, anantenna configured to radiate the RF signal to the DUT. In someembodiments, for each of the at least one emulated channel, the RFtransmitter includes a digital to analog converter that converts theimpaired signal from digital form to analog form. In some embodiments,the RF transmitter includes a variable gain amplifier configured toamplify the RF signal. In some embodiments, the system includes,exterior to the anechoic chamber, a communication tester configured togenerate the at least one transmit signal.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, in a chamber is provided. The system includes,within the chamber, for each of at least one emulated channel, areceiver configured to down-convert a radio frequency, RF, signalreceived from an antenna to produce a down-converted signal for theemulated channel. The system further includes, within the chamber, anemulator core to introduce an impairment in each of at least one replicaof the down converted signal to produce at least one output signal.

In some embodiments, the chamber is one of an anechoic chamber and areverberation chamber. In some embodiments, the impairment is at leastone of an amplitude weight and a temporal shift. In some embodiments,the system further includes, for each of the at least one emulatedchannel, an antenna configured to receive the RF signal from the DUT. Insome embodiments, the system further includes, exterior to the chamber,a plurality of transmitters, each transmitter receiving one of theplurality of output signals. In some embodiments, the system includes,exterior to the chamber, a communication tester to receive and test theplurality of output signals.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of embodiments described herein, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of a known uni-directional boundary arraymeasurement system;

FIG. 2 is a schematic illustration of a known spatial channel emulatorfor a typical conducted radio test;

FIG. 3 is a block diagram of common components of an emulator receiver;

FIG. 4 is a block diagram of common components of an emulatortransmitter;

FIG. 5 is a single emulated downlink channel between a wirelesscommunication tester and a DUT;

FIG. 6 is a single emulated uplink channel between a DUT and a wirelesscommunication tester;

FIG. 7 is a block diagram of a distributed channel emulation system fordownlink signaling;

FIG. 8 is a block diagram of a distributed channel emulation system foruplink signaling;

FIG. 9 is a block diagram of an alternative embodiment of a distributedchannel emulation system for downlink transmissions;

FIG. 10 is a block diagram of an alternative embodiment of a distributedchannel emulation system for uplink transmissions;

FIG. 11 is a block diagram of an embodiment of a distributed channelemulation system for downlink transmissions;

FIG. 12 is a block diagram of an embodiment of a distributed channelemulation system for uplink transmissions;

FIG. 13 a block diagram of a bi-directional node for channel emulationon the downlink and the uplink;

FIG. 14 is a block diagram of a bi-directional dual polarization systemfor channel emulation on the downlink and the uplink;

FIG. 15 is a block diagram of an anechoic chamber having a DUT and aplurality of antennas connected to multiple distributed communicationtester/channel emulator nodes;

FIG. 16 is a block diagram of a dual boundary array system;

FIG. 17 is a flowchart of a first exemplary process for implementing ameasurement system;

FIG. 18 is a flowchart of a second exemplary process for implementing ameasurement system;

FIG. 19 is a flowchart of a third exemplary process for implementing ameasurement system; and

FIG. 20 is a flowchart of a fourth exemplary process for implementing ameasurement system.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of apparatus components andprocessing steps related to electromagnetic measurement systems fortesting devices. Accordingly, the system and method components have beenrepresented where appropriate by conventional symbols in the drawings,showing only those specific details that are pertinent to understandingthe embodiments of the present disclosure so as not to obscure thedisclosure with details that will be readily apparent to those ofordinary skill in the art having the benefit of the description herein.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements.

Some embodiments include a distributed channel emulation system. In someembodiments, functions of a spatial channel emulator are distributedbetween a central location and a remote location. In some embodiments,for example, the up and down converters of the distributed channelemulation system may be located in a remote location, such as in a testchamber, while the emulator core remains in a central location. As usedherein, the remote location may be where antennas of an electromagneticmeasurement system are located. The central location is apart from theremote location and may have a user interface to control tests performedby the electromagnetic measurement system. By distributing components ofthe spatial channel emulator to a remote location, low loss cables canbe used to carry intermediate frequency (IF) signals or baseband signalsfrom the central location to the remote location with much lower loss ascompared with transmission of higher radio frequency (RF) signals.

In some embodiments, the digital to analog conversion on the uplink, andthe analog to digital conversion on the downlink are also located in theremote location with the up and down converters, while the emulator coreremains in the central location.

In some embodiments, the emulator core is also located in the remotelocation. In some embodiments, a wireless communication tester andchannel emulator are located in a remote location, such as in a testchamber, in proximity to each of a plurality of antennas. Eachcombination of wireless communication tester and channel emulator issynchronized with other combinations of wireless communication testerand channel emulator. In some embodiments, a dual boundary array isprovided.

In embodiments described herein, reference will be made to an emulatedchannel. An emulated channel is a channel that is emulated by anelectronic manipulation of signals to emulate the effects of a channelbetween a first device, such as a base station or wireless radio, and asecond device, such as the DUT. For example, in a real worldenvironment, an RF signal from a base station to a wireless device, suchas a cell phone, leaves the base station and bounces off walls ofbuildings and the ground so that an RF signal will arrive at thewireless device from different directions at different times. Also, ifthe wireless device is in motion relative to the source or other objectsin the environment, the RF signal arriving at the wireless device may beshifted in frequency. This is known as Doppler shift. Note that theterm, RF, as used herein encompasses, without limitation, microwave andmillimeter wave frequencies.

The spatial channel emulator described herein can be programmed tointroduce impairments in replicas of a signal from the wirelesscommunication tester to produce signals that emulate the variousimpairments of an RF signal propagating through a real-world channel.The spatial channel emulator may also be programmed to emulate Dopplershift. Similar to the channel effects on the downlink RF signalstransmitted to the DUT, channel effects on the uplink RF signalsreceived from the DUT may also be emulated. That is, on the uplink, thespatial channel emulator may emulate an actual channel between the DUTand a base station by introducing impairments of replicas of a signalreceived from the DUT.

In addition to the impairments introduced by the channel emulator(s),each antenna may be positioned to communicate with the DUT at adifferent angle of arrival. The array of antennas may be two or threedimensional and are generally disposed about a test volume where the DUTis located.

In some embodiments, each antenna 12 in a boundary array system isconnected directly (i.e., with a very short cable) to a broadband radiotransmitter, receiver, or transceiver capable of generating and/orreceiving broadband signals in a desired frequency range. The desiredcommunication signals are aggregated in a low loss or lossless manner tothe other end of the communication link, which may be one or morewireless communication testers 68 or reference radios, an integrateddigital emulation of said testers/radios, or even one or more additionalboundary arrays containing another over-the-air radio communicationdevice.

Thus, when reference is made herein to a wireless communication testeror communication tester, it will be understood by persons of ordinaryskill in the art that such tester is merely representative of a tester,a reference radio, a digitally emulated radio or another boundary arraycontaining an over-the-air radio communication device. The wirelesscommunication tester is capable of sending and receiving communicationsignals that, in some embodiments, are according to a communicationsprotocol that is used by the DUT, such as for example a Wi-Ficommunication protocol or a 3GPP Long Term Evolution (LTE) protocol.

In some embodiments, the RF up-conversion and down conversion segmentsof the associated inputs and outputs of a traditional RF channelemulator are moved to independently powered modules within the testchamber and may be attached directly to antennas with, for example,short RF cables. The power control and associated circuitry may now beapplied directly at the antenna ports, while the baseband/digitalconversion and emulation may remain at a centralized location.

FIG. 7 is a block diagram of distributed spatial channel emulationsystem 61 applied to an anechoic chamber. At a central location 64, anRF/baseband spatial channel emulator portion 59 has a channel emulatorcore 70 a that is configured to introduce impairments in each of atleast one transmit signal received from the wireless communicationtester to produce at least one impaired signal for each of at least oneemulated channel. Each transmit signal may be affected by a differentset of impairments. This enables the test operator to emulate any one ormore of a plurality of different channel models that may includemultipath fading and Doppler shift. At a remote location 65, such as inan anechoic chamber, for each of at least one emulated channel, anup-converter 72 is configured to mix, in a mixer 74, a local oscillator,LO, signal from an LO 76, with an impaired signal of the emulatedchannel to produce a radio frequency, RF, signal. Note that the localoscillator may be replaced by a frequency synthesizer clocked by areference signal such as a 10 mega-Hertz reference signal. Thus,embodiments are not limited to the particular up-conversion circuitshown in FIG. 7.

Note that although an anechoic chamber is shown as the remote location65, the remote location 65 may be another type of chamber, such as areverberation chamber, or may not be a chamber at all. Further, theemulator core 70 may be completely flexible to enable a test operator toemulate any set of channel conditions including multipath fading andDoppler shifting.

In more detail, FIG. 7 shows a wireless communication tester 68 at thecentral location 64 coupled to emulator receivers 78 which are in turncoupled to the emulator core 70 a. The emulator receiver 78 may downconvert the RF signals received from the wireless communications tester68 and convert the down-converted signals to a digital form. Theemulator core 70 a may introduce impairments to one or more of thedigital signals from the emulator receivers 78 and sums the impairedsignals to produce a single composite impaired signal for each one of aplurality of emulated channels. The impairments introduced to thesignals from the emulator receivers 78 may enable a test operator toemulate any type of channel model.

For each emulated channel, an output of an emulator core 70 a may beconverted from a digital signal to an analog signal by a digital toanalog converter (DAC) 80. The output of the DAC 80 may be at anintermediate frequency (IF) or at baseband. The output of the DAC 80 maybe filtered by a filter 82 and amplified by an amplifier 84. The IF orbaseband signal from the amplifier 84 is transported to the remotelocation via a cable, for example. Since, the signal is at a relativelylow intermediate frequency or at baseband, signal losses on the cableare much smaller than if the signal to be carried were at the desiredtest frequency, which is the case in conventional systems, as describedwith reference to FIGS. 1, 5 and 6.

At the remote location 65, the IF or baseband signal is received andamplified by the amplifier 86 and input to the mixer 74 for mixing withthe LO signal to produce an RF signal output. For simplicity, a basicup-conversion circuit is shown in FIG. 7. Persons of ordinary skill inthe art will recognize that different circuits may be implemented toachieve up-conversion of the IF or baseband signal to RF, and thatembodiments are not limited to the particular up-conversion circuitshown in FIG. 7. For example, the local oscillator 76 may be replaced bya synthesizer clocked by a reference signal such as a 10 MHz referencesignal. Alternately, the mixer circuit may also include a frequencymultiplier (not shown) that multiplies a lower frequency LO to a higherfrequency signal to be applied to the mixer 74. Note that the LO signalmay be generated at the remote location or at the central location. TheRF signal may be amplified by a variable gain amplifier 88, which may beimplemented as a series connection of a fixed gain amplifier and anattenuator, for example. The RF signal from the amplifier 88 is fed tothe antenna 12 which radiates the RF signal to the DUT 22.

Thus, some embodiments include a distributed channel emulation system61. The distributed channel emulation system includes, at a centrallocation 64, an emulator core configured to introduce an impairment ineach of at least one transmit signal to produce at least one impairedsignal for each of at least one emulated channel. At a remote location65, for each of at the least one emulated channel, an up-converter isconfigured to up-convert an impaired signal of the emulated channel toproduce a radio frequency (RF) signal. A signal path to transport animpaired signal from the central location 64 to the remote location 65may be a cable, for example.

In some embodiments, an electromagnetic measurement system to performradio frequency, RF, testing of a device under test, DUT, in a chamberis provided, as shown in FIG. 7. In these embodiments, exterior to thechamber, an emulator core 70 a is configured to introduce impairments ineach of at least one transmit signal to produce at least one impairedsignal for each of at least one emulated channel. Within the chamber,for each of the at least one emulated channel, an up-converter 72 isconfigured to receive a local oscillator, LO, signal and to mix the LOsignal with an impaired signal of the emulated channel to produce aradio frequency, RF, signal. In one embodiment, there may be one antennafor each emulated channel to receive the RF signal and radiate the RFsignal to the DUT 22. The chamber at the remote location may be ananechoic chamber or a reverberation chamber, for example.

It is understood that persons of ordinary skill in the art will knowthat an anechoic chamber includes RF absorber on the walls, floor andceiling of the chamber to absorb RF energy, and know that areverberation chamber includes bare reflective shield walls, floor andceiling. Other chambers may be partially lined with absorber. As notedabove, the impairment introduced into a signal by the emulator core mayinclude an amplitude weighting, a temporal shift or other impairment.

FIG. 8 is a block diagram of a distributed channel emulation system 71for uplink signaling applied to an anechoic chamber which includes, at aremote location 65, for each of at least one emulated channel, a downconverter 90 configured to mix a local oscillator, LO, signal from an LO92 with an RF signal to produce a down-converted signal for the emulatedchannel. As noted above with respect to FIG. 7, the LO 92 may bereplaced by a frequency synthesizer clocked by a reference signal orother known method of generating a signal to be applied to the downconverter 90 to down convert the received RF signal. The LO 92 may belocated at the central location or at the remote location. For example,in some embodiments, the LO signal from the LO at the central locationmay be carried to the remote location on a same cable that carries theIF from the remote location to the central location, where the IF and LOsignals may be separated and combined by an optional diplexer, forexample. At a central location 64, an RF/baseband spatial channelemulator portion 69 has an emulator core 70 b that introduce impairmentsin replicas of each of at least one down converted signal received fromthe remote location 65 to produce at least one impaired receive signal.

The impaired receive signals may be coupled to emulator transmitters 94,which up-convert the impaired signals to RF and transmit the impairedreceived signals to a wireless communication tester 68. Note thatalthough FIG. 8 shows a distributed channel emulation system applied toan anechoic chamber, in some embodiments, the remote location 65 is areverberation chamber, or may not be a chamber at all.

In more detail, FIG. 8 shows that an antenna 12 receives anelectromagnetic signal (radio waves) from the DUT 22 and couples thereceived RF signal to an amplifier 96 which may be a low noise amplifier(LNA) and/or a variable gain amplifier (VGA). The output of theamplifier 96 is down-converted to an intermediate frequency (IF) orbaseband. To achieve this, the RF signal may be fed to a mixer 98 whichmixes the RF signal with an LO signal from the LO 92, to produce asignal which is at an intermediate frequency (IF) or at baseband. Thissignal is optionally filtered by a filter 100 and further amplified byan amplifier 102 before being transmitted to the central location. Sincethe signal is at IF or baseband, losses arising from transmitting thesignal between the remote location 65 and the central location 64 arelower than for the conventional systems of FIGS. 1, 5 and 6. At thecentral location 64, the IF or baseband signal from the remote location65 may be amplified by an amplifier 104 and fed to an analog to digitalconverter 106 which outputs a digital signal to the emulator core 70 b.

The emulator core 70 b introduces impairments to replicas of the downconverted digital signal received from the analog to digital converter(ADC) 106 to produce output signals to the emulator transmitters 94.That is, the down-converted signal received from the ADC 106 may bereplicated by the emulator core 70 b and each replica may be impairedwith different one or more impairments. Note that the correspondingsignals from a plurality of remote nodes 90 are independently impairedin the channel emulator core(s) and the resulting signals are summedprior to input of the combined signals to the transmitter 94.

Thus, in some embodiments, a distributed channel emulation system 71 isprovided. At a remote location 65, for each of at least one emulatedchannel, a down converter is configured to mix a local oscillator, LO,signal with an RF signal to produce a down-converted signal for theemulated channel. At a central location 64, an emulator core 70 b isconfigured to introduce an impairment in each of at least one downconverted signal received from the at least one emulated channel toproduce at least one impaired receive signal. At the central location, acommunication tester may be provided and configured to process the atleast one impaired receive signal.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT in a chamber is provided. Within the chamber, foreach of at least one emulated channel, a down-converter 90 is configuredto mix a local oscillator, LO, signal with an RF signal received via anantenna from the DUT to produce a down-converted signal for the emulatedchannel. Exterior to the chamber, an emulator core 70 b is configured tointroduce impairments in replicas of at least one down converted signalreceived from the at least one emulated channel to produce at least oneimpaired receive signal. The chamber at the remote location 65 may be ananechoic chamber or a reverberation chamber, for example.

Note that by moving power amplification directly to the antennas 12, asshown in FIGS. 7 and 8, the same amount of peak power will produce amuch stronger signal at the DUT 22. Conversely, by moving the receiveamplification and down conversion to be near the antenna, the receiversensitivity is greatly improved. By designing the RF inputs and outputsfor the expected over-the-air path loss conditions rather than forconducted testing, the desired amplification can be built directly intothe radio at the remote location. Also, since power control may bemaintained through varying the gain of the amplification, anynon-linearities in the amplification stage is automatically included inthe calibration of the transmitter/receiver configuration and does notintroduce additional uncertainties outside the calibrated instruments.

By moving the up and down conversion to the remote location, the highlosses associated with a long RF cable path can be replaced with lowerloss IF and LO paths. This can also be applied using existing RF channelemulators to produce communication test frequencies at much higherfrequencies than those traditionally supported by these instruments.Thus, for example, an output of the channel emulator of 6 giga-Hertz canbe up-converted at the remote location to 60 GHz.

FIG. 9 is a block diagram of an alternative embodiment of a distributedchannel emulation system 81 for downlink transmissions to a DUT in ananechoic chamber. In this embodiment, the emulator core 70 a is locatedin an RF to digital spatial channel emulator portion 79 at a centrallocation 64 and outputs a digital stream for each emulated channel. TheDAC 80 is at the remote location 65 in a remote transmitter 83 operatingas a vector signal generator. Thus, in this embodiment, at least onetransmit signal is generated at the wireless communication tester 68.The transmit signals from the wireless communication tester 68 arecoupled to emulator receivers 78 at the central location. The emulatorreceivers 78 couple the transmit signals to the emulator core 70 a,which introduces impairments in the transmit signals. Such impairmentsmay include amplitude weighting and time shifting of each of thetransmit signals.

The output of the emulator core 70 a is a digital stream that istransported to the digital to analog converter (DAC) 80 in the remotelocation, which in the example of FIG. 9, is the anechoic chamber. Theoutput of the DAC 80 is an analog signal that may be filtered by thefilter 82 and amplified by the amplifier 86. The amplified, filteredanalog signal is mixed in the mixer 74 with an LO signal from an LO 76to up-convert the signal to an RF signal, that is amplified by anamplifier 88, and transmitted to the antenna 12. The antenna 12 radiatesthe RF signal to the DUT 22. Persons of ordinary skill in the art willrecognized that variations of the circuit 83 may be implemented toachieve digital to analog conversion, up-conversion and amplification.Embodiments are not limited to the example circuit shown in FIG. 9.Further, the LO 76 may be replaced by a direct frequency synthesizerclocked by a reference signal. In some embodiments, the LO signal fromthe LO 76 may itself be up-converted by multiplication to a higherfrequency signal before being applied to the mixer 74.

Thus, in some embodiments, a distributed channel emulation system 81 isprovided that has an emulator core 70 a in a central location 64 and,for each of at least one emulated channel, a signal transmitter 83 in aremote location 65. In other words, in this embodiment, the emulatorcore is at the central location 64 and the emulator transmitter 83 is atthe remote location 65.

FIG. 10 is a block diagram of an alternative embodiment of a distributedchannel emulation system 91 for uplink transmissions from a DUT in ananechoic chamber 14. This embodiment is similar to the embodiment ofFIG. 8, with the difference being that the ADC 106 is located at theremote location 65 in a remote receiver 93. Thus, an RF signal from theDUT 22 is received by the antenna 12 and amplified by the amplifier 96.The amplified RF signal is mixed in a mixer 98 with an LO signal fromthe LO 92 to produce a down converted analog signal for the emulatedchannel. This signal is filtered by the filter 100 and amplified by theamplifier 102. The filtered amplified signal is converted to a digitalsignal by the ADC 106 to produce a digital signal for the emulatedchannel. Persons of ordinary skill in the art will recognized thatvariations of the circuit 93 may be implemented to achieve analog todigital conversion, down-conversion and amplification. Embodiments arenot limited to the example circuit shown in FIG. 10. Further, the LO 92may be replaced by a direct frequency synthesizer clocked by a referencesignal. In some embodiments, the LO signal from the LO 92 may itself beup-converted to a higher frequency signal before being applied to themixer 98.

The digital signal is transmitted to the emulator core 70 b located inan RF digital spatial channel emulator portion 89 at the centrallocation 64 where it may be replicated. The digital signal and itsreplicated signals are each impaired and distributed to a plurality ofemulator transmitters 94. The impairments may include amplitude weightsand time shifting. The emulator transmitters 94 transmit the impairedsignals to the wireless communication tester 68. Note that thecorresponding signals from a plurality of remote nodes 93 areindependently impaired in the channel emulator core(s) and the resultingsignals are summed prior to input of the combined signals to thetransmitter 94.

Thus, in some embodiments, a distributed channel emulation system 91 isprovided that has an emulator core 70 b in a central location 64 and,for each of at least one emulated channel, an ADC and down-converter ina remote location 65. In other words, in this embodiment, the emulatorcore 64 is at the central location and the emulator receiver 93 is atthe remote location 65.

In the embodiments of FIGS. 9 and 10, the entire analog radio (DAC,up-converter and power amplifier for the downlink, and DAC,down-converter and low noise amplifier for the uplink) is located remotefrom the central location 64 and the emulator core 70 is located at thecentral location 64. Communication between the central digital emulationand the digital-to-analog or analog-to-digital converters (DAC/ADC) ofthe transmitter and receiver is all done digitally, and only acentralized reference signal (e.g., 10 MHz) or LO signal may be used tokeep all of the distributed radios in a proper phase-locked conditionand control the operating frequency(ies). Note that a different LO canbe used for the uplink and the downlink.

The distributed radios are essentially vector signal generators oranalyzers capable of converting any digital waveform into the desired RFsignal and vice-versa. The digital signal transferred to the distributedradio in the uplink contains the digital representation of the combinedRF signals that would come from all of the inputs from the wirelesscommunication tester for each path to the particular antenna within thechamber. Likewise, the signal received on that antenna is digitized andreturned to the channel emulator core in the uplink.

Note that the communication between the distributed components in theremote location with the remainder of emulation components at thecentral location may be at IF or baseband, where the losses betweencomponents can be much less than the RF path loss of typical cables.Also, in the uplink configurations, the amplifier 96 being coupleddirectly to the antenna, minimizes or eliminates the need for additionallow noise amplification.

Note that although each of the FIGS. 7-10 show only one direction,uplink or downlink, it is understood that persons of ordinary skill inthe art will be able to implement both directions simultaneously usingisolation circuitry between the antenna 12 and the respectiveup-converters and down-converters. Such isolation circuitry may includea diplexer, isolator, or even separate transmit and receive antennas.The particular isolation circuitry may depend upon the type ofcommunication protocol being tested. For example, Wi-Fi may call for onetype of isolation circuitry, whereas LTE may call for a different typeof isolation circuitry.

Control signals between the central channel emulator core 70 a, 70 b andthe individual transmitters or receivers at the remote location 65 canbe provided by separate digital means such as cables or optical fibers,or even on the cable that carries the baseband or IF digital signal toor from the remote radio modules. Also, power for operating the remotetransmitters and receivers may be applied locally at each radio orcarried on the IF- or LO-carrying cables.

FIG. 11 is a block diagram of an embodiment of a distributed channelemulation system 101 having, at a central location 64, emulatorreceivers 78 within an RF to digital converter portion 99, and at aremote location 65, for each emulated channel, an emulator core 70 c,DAC 80 and up-converter. Thus, in this embodiment, a signal carrier 110such as a cable, carries digital signals from the plurality of emulatorreceivers 78 at the central location to a least one emulator core 70 cof an RF output channel emulator portion 103. The signal carrier 110 maybe a single cable or a plurality of cables. The output of the emulatedcore 70 c is an impaired signal which is a combination of impairedsignals from the plurality of emulator receivers 78. The impairments caninclude amplitude weights and/or time-shifts and/or other impairments.

The output of an emulator core 70 c is input to the transmitter chainincluding DAC 80, filter 82, amplifier 86, mixer 74 and VGA 88, whichoperates as described above with reference to FIG. 9. The up-convertedamplified signal output by the VGA 88 is coupled to the antenna 12,which radiates the RF signal to the DUT 22.

Thus, in some embodiments, a distributed channel emulation system 101 isprovided that has at least one emulator receiver 78 in a centrallocation 64 and, for each of at least one emulated channel, an emulatorcore 70 c, a DAC and up-converter in a remote location 65.

FIG. 12 is a block diagram of an embodiment of a distributed channelemulation system 111 having, at a central location 64, emulatortransmitters 94 in a digital to RF converter portion 109, and at aremote location 65, for each emulated channel, an emulator core 70 d ofan RF input channel emulator portion 113. In this embodiment, a signalcarrier 110 such as a cable, carries digital signals from the pluralityof emulator cores 70 d at the remote location to a plurality of emulatortransmitters 94. Note that the corresponding signals from a plurality ofremote nodes 113 are independently impaired in the channel emulatorcore(s) and the resulting signals are summed prior to input of thecombined signals to the transmitter 94.

In operation, for each emulated channel, an RF signal is received froman antenna 12, and amplified by the amplifier 96. The amplified RFsignal from amplifier 96 is down-converted by mixing it with a LO signalfrom the LO 92 in the mixer 98. The down-converted signal is filtered bythe filter 100, amplified by the amplifier 102 and converted from analogto digital form by ADC 106. The digital signal output by ADC 106 iscoupled to an emulator core 70 d. The emulator core impairs the digitalsignal and replications of the digital signal by impairments to producea plurality of impaired output signals that are combined withcorresponding signals from other emulator cores 70 d (not shown) andcarried by signal carrier 110 to the plurality of emulator transmitters94 at the central location 64. These signals received from the emulatortransmitters 94 are coupled to the wireless communication tester 68.

Thus, in some embodiments, a distributed channel emulation system isprovided that has at least one emulator transmitter in a centrallocation 64 and, for each of at least one emulated channel, an emulatorcore, an ADC and a down-converter in a remote location 65.

In the configurations of FIGS. 11 and 12, the digital signal processingcomponents of the channel emulator are in the distributed nodes of theremote location 65, thereby giving each node ability to generate its ownemulated channel between the wireless communication tester 68 and thetest volume where the DUT 22 is located. The centralized portion of thechannel emulator then contains only the components used to combine thedigital signals and convert from digital to analog to RF for interfaceto the communication tester, and any centralized control and LO and/orreference signals.

Note, however, that the LO may also be produced by a single module inthe remote location of the distributed system and shared among modules,eliminating the need for transfer of that signal outside the chamber inthe case where it is not also used for the RF connection between thechannel emulator and communication tester.

The digital communication used to transfer the real-time streamingwaveform between the central location and the remote location may becarried through electrical cables specific to the chosen high speedinterface (e.g. MXI-2, HSSI, custom, etc.) or fiber optic cables,thereby eliminating the RF interactions and shielding issues associatedwith electrical cables. In any of the above implementations, the RFconnections between the communication tester and channel emulator couldbe replaced by baseband or IF communication or digital informationtransfer to the DAC or from the ADC.

Note that the embodiments of FIGS. 7 and 8 can be combined to provide abi-directional system. Similarly, the embodiments of FIGS. 9 and 10 canbe combined to provide a bi-directional system. Also, the embodiments ofFIGS. 11 and 12 can be combined to provide a bi-directional system.

FIG. 13 is a block diagram of a bi-directional node 121 for channelemulation on the downlink and the uplink, all contained within a remotelocation 65, such as an anechoic chamber 14. A software-defined orchipset-based communication tester 112 provides transmit signals for thedownlink and receives output signals for the uplink. The transmitsignals from the communication tester 112 are coupled to an emulatorcore 70 e which introduces an impairment to replicas of at least one ofthe transmit signals to produce an impaired signal for an emulatedchannel.

The impaired signal from the emulator core 70 e is a digital signal thatis coupled to the transmitter 114, where the digital signal is convertedto analog, up-converted to RF and amplified. The amplified RF signalfrom the transmitter 114 is sent to a signal isolator 118 which couplesthe amplified RF signal to the antenna 12 while preventing the amplifiedRF signal from entering the receiver 116 of the uplink path. The antenna12 radiates the RF signal to the DUT 22. Note that the type of signalisolator 118 may depend on the communication protocol of the DUT 22.Note also that the communication tester 112 may produce digitalcommunication signals at base band rather than producing RF signals asin conventional wireless communication testers. Accordingly, thecommunication tester 112 need not include RF components such as an RFisolator between the transmit and receive ports of the communicationtester.

On the uplink, the antenna 12 receives an RF signal from the DUT 22 andcouples the received RF signal to the isolator 118. The isolator 118couples the received RF signal to the receiver 116 while preventing thereceived RF signal from entering the transmitter 114. The receiver 116amplifies and down-converts the received RF signal, and converts thedown-converted signal to digital form. The output of the receiver 116 iscoupled to an emulator core 70 f. The emulator core 70 f impairs thesignal received from the receiver 116 and may also produce and impairreplications of this signal, to produce at least one impaired signalthat is coupled to the communication tester 112.

As shown in FIG. 13, in some embodiments, the impaired signals from theemulator core may be transmitted to the communication tester and alsosent to additional nodes identical to the node of FIG. 13 to be combinedwith the impaired signals from the emulators of those additional nodes.Likewise, the impaired signals from the additional nodes are received bythe node of FIG. 13 and added to the signals from the emulator core 70 fof FIG. 13. Also synchronization signals are coupled to the node of FIG.13 and to the additional nodes to ensure that the signals generated bythe communication testers in each node have the same content and timing.Also, control signals received from a user interface and controller aredistributed to the node of FIG. 13 and additional nodes to enable a userto control the communication testers of the nodes.

FIG. 14 is a block diagram of a bi-directional dual polarization systemfor channel emulation on the downlink and the uplink, all containedwithin a remote location 65, such as an anechoic chamber. The softwaredefined or chipset based wireless communication tester 112 providestransmit signals to the emulator core for the downlink and receivesoutput signals from the emulator core for the uplink. The transmitsignals from the wireless communication tester 112 are coupled to anemulator core 70 g which may introduce an impairment to each of twotransmit signals to produce two signals for two emulated channels, eachchannel corresponding to a different polarization. In other words, eachof the two signals corresponds to one of two polarizations which may beorthogonal.

Each of the two signals are fed to one of two transmitters 114 a and 114b. Each transmitter converts the signal it receives to analog form,up-converts the signal to RF and couples the RF signal to one of twoisolators 118 a and 118 b. The signal isolator 118 a transmits the RFsignal it receives to a vertical polarized antenna element of theantenna 12. The signal isolator 118 b transmits the RF signal itreceives to a horizontal polarized antenna element of the antenna 12.Persons of ordinary skill in the art will recognize that vertical andhorizontal polarizations are but examples of different polarizationsthat can be transmitted.

For the uplink, each of two orthogonally polarized antenna elements ofantenna element 12 couple RF signals received from the DUT 22 toisolators 118 a and 118 b. Isolators 118 a and 118 b couple the receivedRF signals to receivers 116 a and 116 b. Each receiver 116 amplifies itsrespective received RF signal and down-converts the received RF signalto an IF signal or to a baseband signal. Each receiver has an ADC thatconverts its received down-converted signal to digital form. The outputsof the receivers 116 are input to an emulator core 70 h which mayintroduce different impairments to the received signals and couples theimpaired signals to the wireless communication tester 112.

As discussed above with reference to FIG. 13, the impaired signals fromthe emulator core 70 h of the node of FIG. 14 may be combined withcorresponding impaired signals from additional nodes and input to thecommunication tester 112. The impaired signals from the emulator core 70h of the node of FIG. 14 may also be sent to the additional nodes to besimilarly combined with the impaired signals from the emulators of theadditional nodes. Also synchronization signals are coupled to the nodeof FIG. 14 and to the additional nodes to ensure that the signalsgenerated by the communication testers in each node have the samecontent and timing. Also, control signals received from a user interfaceand controller are distributed to the node of FIG. 14 and additionalnodes to enable a user to control the communication testers of thenodes.

Thus, some embodiments provide a complete radio and channel emulatorbehind each antenna 12 at the remote location, capable of performing allradio communication and multipath emulation for single or dualpolarization at different angles of arrival. The radio and channelemulator can be implemented entirely by software executed by aprocessor, such as a digital signal processor, or may be implemented ina combination of hardware, such as application specific hardware, andsoftware.

Thus, in the implementations of FIGS. 13 and 14 the communication testerand channel emulator are merged into a single possibly software-defined,radio for a desired radio communication protocol. The desired channelemulation for the associated path to the test volume would be applied tothe digital communication prior to the analog conversion on the downlinkand before the decoding of the digitized signal on the uplink. Digitaland LO synchronization and control signals could be shared between thedistributed nodes, and a single control interface could be made back toa centralized PC or other control/user interface.

Even in the case where a chipset implementation is used to implement thecommunication tester or is more practical for the wireless protocolcomponents being implemented by the communication tester, a chipsetimplementation would be realizable with minimal modifications to currentoff-the-shelf communication testers with basic fading/channel emulationcapabilities. The main task is to synchronize the protocol components(software or chipsets) so that they are producing the same digital dataat the same time and then apply the digital fading for each separatepath to the resultant digital signal prior to converting it to RF.

On the downlink side, the digitized data is altered by the digitalchannel emulation prior to being received by each radio. The digitizedresults can be summed together and processed as a single total result.The net result is that on the downlink side, each chipset in each nodewould be creating the signal independently with appropriatesynchronization, while on the uplink side, the digitized results fromeach receiver would be combined and fed to the receiver of only a singlechipset to decode the received protocol with the sum of the fadingeffects from all of the emulated channels.

Since the distributed communication tester is really emulating a singletransceiver end point, the signals should still have a common endpoint.On the transmit side, that may be as simple as configuring each node totransmit the same data and keep them synchronized. However, on thereceive side, the behavior of the radio receiver depends on the total ofthe signals from all nodes. For fully digital implementations, someportion of the received signal processing may be done in each node priorto combining, while for a chipset based implementation, the signalsshould be aggregated digitally at one node and then sampled by a singlechipset to process the final received signal. Alternately, multiplechipsets can sample the aggregated signal and some composite average orsum of the results of each chipset output be used to determine the finalreceived signal.

FIG. 15 is a block diagram of an example anechoic chamber having a DUT22 and a plurality of antennas 12. Each antenna 12 may includedifferently polarized antenna elements. Note that the DUT 22 may bepositioned on a positioning system that rotates or otherwise moves withrespect to the antennas 12. Connected to each antenna 12 is abi-directional combination 120 of a communication tester 68 and channelemulator 70. The outputs of the combinations 120, which may be basebandsignals, are transported by a cable 122 in and out of the remotelylocated chamber to a central location that provides a user interface.Control signals to control the communication tester and channel emulatorof each combination 120 may also be transported by the cable 122. Notethat the configuration of combinations 120 is shown inside an anechoicchamber but in some embodiments, the combinations 120 may not be locatedin a chamber at all, or may be located in a reverberation chamber, forexample. Note also that in some embodiments the antennas 12 may besingle polarization antennas or dual polarized antennas.

By making each antenna of the boundary array into a software definedradio designed for over-the-air communication, the relatively low pathloss associated with the short range lengths typically used for thistesting means that the radio in each node does not require exceptionalcapabilities to address the associated path losses. Here, a node refersto the combination of wireless communication tester and channelemulator.

In one embodiment, the system 121 becomes one radio (the DUT)communicating with a large number of radios (the array), allsimultaneously. Note that for a completely software definedimplementation, the number of MIMO streams is only limited by theprocessing resources necessary to emulate them. In the configuration ofFIG. 16, the combinations of channel emulators and communication testersmay all be synchronized by a signal at the remote location or in acentral location.

Note that in the embodiments above, the local oscillator (LO) may belocated at a central location and distributed to the mixers at theremote location or a LO may be located in proximity of each mixer at theremote location. The LO signal may, in some embodiments, be multipliedupward before being input to a respective mixer of the remote up ordown-converter, resulting in an LO frequency being well below thedesired operating RF. The LO signal frequency may also be the same fordifferent emulated channels or may be different for different emulatedchannels (e.g. for LTE carrier aggregation and similar approaches).

Further, the LO signal frequencies may be different on the uplink thanon the downlink. As noted above, the LO signal may be coupled on thesame cable that carries the up-converted or down-converted signals usinga diplexer, circulator or isolator. Also, the LO signal may be areference signal, for example, a 10 MHz reference clock, that eachdistributed front end converts to a target LO frequency for mixing inthe respective mixer 74, 98.

FIG. 16 is a diagram of an embodiment of a dual boundary array toemulate full spatial communication between two endpoints. The dualboundary array includes a first boundary array 126 and a second boundaryarray 128 connected by a digital connection 130, for example. Asmentioned above, the distributed nodes on one side (or both) could beconducted connections to a reference radio or multiple devices undertest where full multi-port network emulation evaluation is desired (e.g.massive MIMO). Optionally, one may implement a distributed node on oneend and a centralized node on the other end, as already described above.In FIG. 16, the channel emulators 132 and 133 emulate channels byintroducing impairments to their respective received or transmittedsignals. For example, the DUT 22 may be a base station and the DUT 23may be a wireless phone. In this case, on the downlink, the base stationDUT 22 generates communication signals to be transmitted to the wirelessphone DUT 23. On the uplink, the wireless phone DUT 23 generatescommunication signals to be transmitted to the base station DUT 22. Onthe downlink, channel emulators 132 and 133 introduce impairments to thedownlink signals from the base station DUT 22 and on the uplink, channelemulators 132 and 133 introduce impairments to the uplink signals fromthe wireless phone DUT 23.

In some embodiments, the antennas 13 can be replaced by DUTs connecteddirectly to the channel emulators 133. In some embodiments, both theantennas 13 and antennas 12 may be replaced by DUTs. Thus, in someembodiments, an array of individual radios (e.g. mobile handsets) may beconnected to an array of individual channel emulator nodes which are inturn inter-connected with a boundary array with a DUT (e.g. a massiveMIMO base station), or another array of individual nodes connected toother radios (e.g. for mesh network testing). Also, in some cases theconfiguration of channel emulators 132 and/or 133 may not be enclosed inan anechoic chamber when the DUTs are connected directly to the channelemulators, for example.

Thus, in some embodiments, one set of remote nodes are connected toanother set of remote nodes at a different location. In someembodiments, these remote nodes may consist of up/down convertercomponents routed through a central channel emulator. In someembodiments, the communication may be digital between nodes withtransmitter and/or receiver components. In some embodiments, the remotenodes may also contain channel emulator components. In some embodiments,sets of remote nodes are directly interconnected. In some embodiments,the remote nodes are connected to antennas. In some embodiments, remotenodes are contained within a chamber. In some embodiments, some or allof the remote nodes are connected to wireless communication devices.

FIG. 17 is a flowchart of an exemplary process for implementing ameasurement system. The process includes providing a plurality of nodes,each node including a combination of a communication tester configuredto generate a communication signal and a channel emulator configured toemulate a channel (block S100). The process further includes providing auser interface configured to enable a user to control at least one ofthe plurality of nodes (block S102).

FIG. 18 is flowchart of another exemplary process for implementing ameasurement system. The process includes providing a plurality of nodes,each node having a combination of a channel emulator configured toreceive and impair a communication signal and a communication testerconfigured to receive an impaired communication signal (block S104). Theprocess further includes providing a user interface configured to enablea user to control at least one of the plurality of nodes (block S106).

FIG. 19 is a flowchart of an exemplary process for implementing ameasurement process. The process includes providing at a centrallocation an emulator core configured to introduce an impairment in atransmit signal to produce an impaired signal for an emulated channel(block S108). The process further includes providing at a remotelocation, an up-converter configured to up-convert an impaired signal toproduce an RF signal (block S110).

FIG. 20 is a flowchart of another exemplary process for implementing ameasurement system. The process includes providing at a remote location,for each of at least one emulated channel, a down-converter configuredto down-convert a radio frequency, RF, signal to produce adown-converted signal (block S112). The process further includesproviding at a central location, an emulator core configured tointroduce an impairment in the down-converted signal to produce animpaired receive signal (block S114).

Thus, some embodiments include a distributed channel emulation systemimplementing a downlink channel, including at a central location, anemulator core configured to introduce an impairment in each of at leastone transmit signal to produce at least one impaired signal for each ofat least one emulated channel. The system includes, at a remotelocation, for each of at the least one emulated channel, an up-converterconfigured to mix a local oscillator, LO, signal with an impaired signalof the emulated channel to produce a radio frequency, RF, signal.

In some embodiments, the system includes a signal path to transport atleast one impaired signal from the emulator core to the up-converter atthe remote location. In some embodiments, the system includes, at thecentral location, a communication tester configured to generate the atleast one transmit signal. In some embodiments, the remote location iswithin a test chamber and the central location is exterior to the testchamber. In some embodiments, the system also includes, at the remotelocation, for each of the at least one emulated channel, a digital toanalog converter to convert the impaired signal to an analog signal tobe mixed with the LO signal.

In some embodiments, a distributed channel emulation system implementingan uplink channel is provided. At a remote location, for each of atleast one emulated channel, a down converter is configured to mix alocal oscillator, LO, signal with an RF signal to produce adown-converted signal for the emulated channel. At a central location,an emulator core is configured to introduce an impairment in each of atleast one down converted signal received from the at least one emulatedchannel to produce at least one impaired receive signal.

In some embodiments, the system includes, between the central locationand the remote location, a signal path to transport at least oneimpaired signal from the emulator core to the up-converter at the remotelocation. In some embodiments, the system includes, at the centrallocation, a communication tester configured to process the at least oneimpaired receive signal. In some embodiments, the remote location iswithin a test chamber and the central location is exterior to the testchamber. In some embodiments, the system further includes, at the remotelocation, for each of the at least one emulated channel, an analog todigital converter to convert the down-converted signal to a digitalsignal.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, in a chamber is provided. Within the chamber,for each of at least one emulated channel, a first emulator core isconfigured to introduce an impairment in each of at least one transmitsignal to produce an impaired signal, and a transmitter is configured toconvert the impaired signal to a radio frequency, RF, signal to betransmitted by an antenna.

In some embodiments, the chamber is one of an anechoic chamber and areverberation chamber. In some embodiments, the impairment is at leastone of an amplitude weighting and a temporal shift. In some embodiments,the system further includes, within the chamber, for each of the atleast one emulated channel, a communication tester configured to emulatethe at least one transmit signal. In some embodiments, the systemfurther includes, within the chamber, for each of the at least oneemulated channel, a receiver configured to receive a radio frequency,RF, signal from the antenna and convert the received RF signal to adown-converted signal, and a second emulator core to introduce animpairment in each of at least one replica of the down converted signalto produce at least one output signal. In some embodiments, within thechamber, for each of the at least one emulated channel, a communicationtester is configured to receive and test the at least one output signal.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, in a chamber is provided. Within the chamber,for each of a plurality of emulated channels, a first emulator core isconfigured to introduce an impairment in each of at least one transmitsignal to produce a first impaired signal and a second impaired signal.Also within the chamber, a first transmitter is configured to convertthe first impaired signal to a first radio frequency, RF, signal to betransmitted by an antenna according to a first polarization, and asecond transmitter configured to convert the second impaired signal to asecond RF signal, to be transmitted by the antenna according to a secondpolarization.

In some embodiments, the chamber is one of an anechoic chamber and areverberation chamber. In some embodiments, the impairment is at leastone of an amplitude weighting and a temporal shift. In some embodiments,the system further includes, within the chamber, for each of the atleast one emulated channel, a communication tester configured to emulatethe plurality of transmit signals. In some embodiments, each antennaincludes a pair of orthogonally polarized antenna elements.

In some embodiments, the system further includes, within the chamber,for each of the at least one emulated channel: a first receiverconfigured to receive a first RF signal from the antenna according to afirst polarization and convert the received first RF signal to a firstdown-converted signal; a second receiver configured to receive a secondRF signal from the antenna according to a second polarization andconvert the second RF signal from the antenna to second down-convertedsignal; and a second emulator core to introduce a different delay spreadin each of at least one replica of the first and second down convertedsignals to produce at least one output signal. In some embodiments, thesystem further includes, within the chamber, for each of the at leastone emulated channel, a wireless communication tester configured toreceive and test the at least one output signal.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, is provided. The system includes a plurality ofnodes, each node having a combination of a communication testerconfigured to generate a communication signal and a channel emulatorconfigured to emulate a channel.

In some embodiments, the communication testers in the plurality of nodesare synchronized in time. In some embodiments, the communication testersare synchronized in content. In some embodiments, each combinationfurther comprises an antenna coupled to the channel emulator of thecombination. In some embodiments, the combinations, the antennas and theDUT are located within a chamber. In some embodiments, the chamber isone of an anechoic chamber and a reverberation chamber.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, is provided. The system includes a plurality ofnodes, each node having a combination of a channel emulator configuredto receive a signal and emulate a channel and a communication testerconfigured to receive a communication signal.

In some embodiments, the communication testers are synchronized in time.In some embodiments, each combination further includes an antennacoupled to the channel emulator. In some embodiments, at least oneantenna is a dual-polarized antenna. In some embodiments, thecombinations, the antennas and the DUT are located within a chamber. Insome embodiments, the chamber is one of an anechoic chamber and areverberation chamber. In some embodiments, the outputs of the channelemulators are summed or averaged in at least one node.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT is provided. The system includes, at a centrallocation, an emulator core configured to introduce an impairment in eachof at least one transmit signal to produce a digital impaired signal;and at a remote location, a transmitter configured to convert thedigital impaired signal to an analog RF signal.

In some embodiments, the transmitter includes a digital to analogconverter and a frequency up-converter. In some embodiments, the systemfurther includes, at the central location, a communication testerconfigured to generate the at least one transmit signal. In someembodiments, the remote location is within a test chamber and thecentral location is exterior to the test chamber. In some embodiments,the system further includes a cable configured to carry the digitalimpaired signal from the central location to the remote location.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, is provided. The system includes, at a remotelocation, a receiver configured to convert an analog RF signal to adigital signal; and at a central location, an emulator core configuredto introduce an impairment in each of at least one replica of thedigital signal to produce at least one impaired signal.

In some embodiments, the receiver includes a frequency down converterand an analog to digital converter. In some embodiments, the systemfurther includes, at the central location, a communication testerconfigured to receive the at least one impaired signal. In someembodiments, the remote location is within a test chamber and thecentral location is exterior to the test chamber. In some embodiments,the system further includes a cable configured to carry the digitalsignal from the remote location to the central location.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT, is provided. The system includes, at a remotelocation, for each of at least one emulated channel: a first emulatorcore configured to introduce an impairment in each of at least onetransmit signal to produce an impaired signal; and a transmitterconfigured to convert the impaired signal to a radio frequency, RF,signal.

In some embodiments, the transmitter includes a digital to analogconverter and a frequency up-converter. In some embodiments, the systemincludes, at a central location, a communication tester configured togenerate the at least one transmit signal. In some embodiments, theremote location is within a test chamber and the central location isexterior to the test chamber. In some embodiments, the system furtherincludes a cable configured to carry the impaired signal from thecentral location to the remote location.

In some embodiments, an electromagnetic measurement system to test adevice under test, DUT is provided. The system includes, at a remotelocation, for each of at least one emulated channel, a receiverconfigured to receive a radio frequency, RF, signal and convert thereceived RF signal to a down-converted signal; and an emulator coreconfigured to introduce an impairment in each of at least one replica ofthe down converted signal to produce at least one output signal.

In some embodiments, the receiver includes a frequency down converterand an analog to digital converter. In some embodiments, the systemincludes, at a central location, a communication tester configured toprocess the at least one output signal. In some embodiments, the remotelocation is within a test chamber and the central location is exteriorto the test chamber. In some embodiments, the system includes a cableconfigured to carry the impaired signal from the remote location to thecentral location.

Embodiments advantageously provide a method and system for measuring adevice under test. In some embodiments, a method of implementing ameasurement system is provided. The method includes providing aplurality of nodes, each node including a combination of a communicationtester configured to generate a communication signal and a channelemulator configured to emulate a channel, and providing a user interfaceconfigured to enable a user to control at least one of the plurality ofnodes.

In some embodiments, the method further includes providing signalcommunication with the plurality of nodes to synchronize thecommunication testers in time. In some embodiments, the method furtherincludes providing signal communication with the plurality of nodes tosynchronize the communication testers in content. In some embodiments,the method further includes locating the plurality of nodes within atest chamber. In some embodiments, the communication signals are digitalsignals. In some embodiments, the method further includes at each node,an antenna. In some embodiments, the method further includes disposingthe nodes about a test volume.

In some embodiments a method of implementing a measurement system isprovided. The method includes providing a plurality of nodes, each nodehaving a combination of a channel emulator configured to receive andimpair a communication signal and a communication tester configured toreceive an impaired communication signal. The method also includesproviding a user interface configured to enable a user to control atleast one of the plurality of nodes.

In some embodiments, the method further includes locating the pluralityof nodes within a test chamber. In some embodiments, the method furtherincludes providing at each node, an antenna. In some embodiments, themethod further includes disposing the nodes about a test volume. In someembodiments, each communication tester is configured to receive digitalsignals from a corresponding channel emulator. In some embodiments, atleast one communication tester is configured to receive digital signalsfrom a plurality of channel emulators.

In some embodiments, another method of implementing a measurement systemis provided. The method includes providing at a central location anemulator core configured to introduce an impairment in a transmit signalto produce an impaired signal for an emulated channel. The methodfurther includes providing at a remote location, an up-converterconfigured to up-convert an impaired signal to produce a radiofrequency, RF, signal.

In some embodiments, the method further includes at the centrallocation, a communication tester configure to generate the transmitsignal. In some embodiments, the remote location is within a testchamber and the central location is exterior to the test chamber.

In some embodiments, another method of implement a measurement system isprovided. The method includes providing at a remote location, for eachof at least one emulated channel, a down-converter configured todown-convert a radio frequency, RF, signal to produce a down-convertedsignal. The method further includes providing at a central location, anemulator core configured to introduce an impairment in thedown-converted signal to produce an impaired receive signal.

In some embodiments, the method further includes at the centrallocation, a wireless communication tester configured to process theimpaired receive signal. In some embodiments, the remote location iswithin a test chamber and the central location is exterior to the testchamber. In some embodiments, the down-converted signal is digitizedprior to introducing the impairment.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,and/or computer program product. Accordingly, the concepts describedherein may take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.”Furthermore, the disclosure may take the form of a computer programproduct on a tangible computer usable storage medium having computerprogram code embodied in the medium that can be executed by a computer.Any suitable tangible computer readable medium may be utilized includinghard disks, CD-ROMs, electronic storage devices, optical storagedevices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer (to therebyform a special purpose computer), special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to support claims to any such combination orsubcombination.

It will be appreciated by persons skilled in the art that the presentembodiments are not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope of thefollowing claims.

What is claimed is:
 1. An electromagnetic measurement system configuredto test a device under test, DUT, in a chamber, the system comprising: achamber; a plurality of antennas within the chamber; within the chamber,for each antenna of the plurality of antennas: a communication testerconfigured to generate at least one transmit signal; a first emulatorcore configured to introduce an impairment in each of at least onetransmit signal to produce a first impaired signal and a second impairedsignal; and a first transmitter connected to the antenna and configuredto convert the first impaired signal to a radio frequency, RF, signal tobe transmitted by the antenna according to a first polarization; and asecond transmitter connected to the antenna and configured to convertthe second impaired signal to a second RF signal to be transmitted bythe antenna according to a second polarization.
 2. The system of claim1, further comprising, for each of the plurality of antennas, the firstand second transmitters include a digital to analog converter thatconverts an impaired signal from digital form to analog form.
 3. Thesystem of claim 1, wherein each antenna includes a pair of orthogonallypolarized antenna elements.
 4. The system of claim 1, wherein animpairment is at least one of an amplitude weighting and a temporalshift.
 5. The system of claim 1, wherein the chamber is one of ananechoic chamber and a reverberation chamber.
 6. The system of claim 1,further comprising, within the chamber, for each of the plurality ofantennas: a first receiver configured to receive a first RF signal fromthe antenna according to a first polarization and convert the receivedfirst RF signal to a first down-converted signal; a second receiverconfigured to receive a second RF signal from the antenna according to asecond polarization and convert the second RF signal from the antenna toa second down-converted signal; a second emulator core configured tointroduce an impairment in each of at least one replica of the first andsecond down converted signals to produce at least one output signal; andthe communication tester configured to receive and process the at leastone output signal.
 7. An electromagnetic measurement system to test adevice under test, DUT, in a chamber, the system comprising, within thechamber for each of at least one emulated channel: a first receiverconfigured to receive a first RF signal from an antenna according to afirst polarization and convert the received first RF signal to a firstdown-converted signal; a second receiver configured to receive a secondRF signal from the antenna according to a second polarization andconvert the second RF signal from the antenna to a second down-convertedsignal; a first emulator core to introduce a different delay spread ineach of at least one replica of the first and second down convertedsignals to produce at least one output signal; and a communicationtester to receive and process the at least one output signal.
 8. Thesystem of claim 7, further comprising, within the chamber, for each ofthe plurality of antennas: the communication tester configured togenerate at least one transmit signal; a first emulator core configuredto introduce an impairment in each of at least one transmit signal toproduce a first impaired signal and a second impaired signal; and afirst transmitter configured to convert the first impaired signal to afirst radio frequency, RF, signal to be transmitted by the antennaaccording to a first polarization; a second transmitter configured toconvert the second impaired signal to a second RF signal, to betransmitted by the antenna according to a second polarization.
 9. Anelectromagnetic measurement system configured to test a device undertest (DUT), the system comprising: in close proximity to each of aplurality of antennas; a wireless communication tester configured to atleast one of: generate and transmit a communication signal; and receiveand process an incoming impaired signal; and a first emulator coreconfigured to impair a communication signal generated by the wirelesscommunication tester to produce an outgoing impaired signal; a secondemulator core configured to impair a received signal to produce anincoming impaired signal; a pair of transmitters, each configured toreceive the outgoing impaired signal and produce an outgoing radiofrequency (RF) signal, one for each of two polarizations; and a pair ofreceivers, each configured to receive a different one of two differentpolarized signals from at least one antenna and to present the twodifferent polarized signals to the second emulator core to be impairedto produce the incoming impaired signal.
 10. The system of claim 9,further comprising a controller located remote from the plurality ofantennas, the controller configured to synchronize the first emulatorsand to synchronize the second emulators.
 11. The system of claim 10,wherein the first emulators are synchronized differently from the secondemulators.
 12. The system of claim 9, wherein the wireless communicationtesters, the first and second emulator cores, and the first and secondpairs of transmitters are located within a test chamber in proximity tothe antennas and remote from a controller located exterior to the testchamber and configured to control at least the wireless communicationtesters.
 13. The system of claim 9, wherein each of the plurality ofantennas is a dual polarized antenna.
 14. The system of claim 9, furthercomprising a first signal isolator coupled to a first one of the pair oftransmitters and a first one of the pair of receivers, and a secondsignal isolator coupled to a second one of the pair of transmitters anda second one of the pair of receivers.
 15. The system of claim 9,wherein the first and second emulator cores are associated with one of adual polarized antenna and with a pair of orthogonally polarized antennaelements.
 16. The system of claim 9, wherein the first and secondemulator cores associated with an antenna are in communication withthird and fourth emulator cores associated with another antenna.
 17. Anelectromagnetic measurement system configured to test a device undertest (DUT) within a test chamber, the system comprising: exterior to achamber that encloses a DUT, a controller configured to enable a user toselect impairments in each of a plurality of emulated channels; interiorto the test chamber, in proximity to each of a plurality of antennas: awireless communication tester configured to one of: generate andtransmit at least one communication signal; and receive and process atleast one incoming impaired signal; and a first emulator core configuredto impair at least one communication signal generated by the wirelesscommunication tester to produce at least one outgoing impaired signal; asecond emulator core configured to impair at least one incoming radiofrequency (RF) signal to produce at least one incoming impaired signal;a first pair of transmitters configured to convert the at least oneoutgoing impaired signal to two outgoing RF signals, each outgoing RFsignal to be transmitted according to different polarizations; and afirst pair of receivers, each configured to receive a different one oftwo differently polarized signals from at least one antenna and topresent the two differently polarized signals to the second emulatorcore to be impaired to produce the at least one incoming impairedsignal.
 18. The system of claim 17, wherein the plurality of wirelesscommunication testers are synchronized by a synchronization signaldistributed to the wireless communication testers.
 19. The system ofclaim 17, wherein the first emulator cores are synchronized to a firstcommon synchronization signal and the second emulator cores aresynchronized to a second common synchronization signal.
 20. The systemof claim 17, wherein each of the plurality of antennas is formed by apair of orthogonally polarized antenna elements.